Reusable Functions

composition.js

const foo = x => x + 2;
const bar = x => x * 3;

console.log(foo(bar(5)))

const scream = str => str.toUpperCase()
const exclaim = str => `${str}!`
const repeat = str => `${str} ${str}`;

console.log(repeat(exclaim(scream('hololo'))))

// lets do HTMLBaseFontElement
const compose = (...fns) => x =>
    fns.reduceRight((acc,fn) => fn(acc), x)

const withExuberance = compose(repeat, exclaim, scream)
console.log(withExuberance('hololo hololo'))

const pipe = (...fns) => x => 
fns.reduce((acc,fn)=>fn(acc),x)

const withExuberance2 = pipe(
    scream, exclaim, repeat
)

console.log(withExuberance2('lolo'))

currying.js

function sum(x) {
    return function(y) {
        return x + y;
    }
}
console.log(sum(3,2)) // second variable is ignored
const addThree = sum(1)
console.log(addThree(3))

const sum2 = x => y => x+y;

HOF.js

// Higher order Functions

// 1. Accept a function as an argument
// 2. Returns a new function

const withCount = fn => {
    let count = 0;
    return (...args) => {
        console.log(`calls count ${++count}`);
        return fn(...args);
    }
}

const add = (x,y) => x + y;


const countedAdd = withCount(add)
console.log(countedAdd(1,2))
console.log(countedAdd(2,3))
console.log(countedAdd(2,5))
console.log(countedAdd(3,6))
console.log(countedAdd(4,2))

immutableData.js

const mutableArray = [1,2,3]
const rAA = mutableArray;
rAA.push(4);
console.log(mutableArray);

const mutableObject = {foo: 'bar'}
const rAO = mutableObject;
rAO.foo = 'baz';
console.log(mutableObject)


const push = value => array => {
    const clone = [...array];
    clone.push(value)
    return clone;
}
// for Immutable array
const immutableArray = [1,2,3];
const rAAI = push(4)(immutableArray)
console.log(immutableArray)
console.log(rAAI)


class MutableGlass {
    constructor(content, amount) {
        this.content = content;
        this.amount = amount;
    }
    takeDrink(value) {
        this.amount = Math.max(this.amount - value, 0);
        return this
    }
}

const mg1 = new MutableGlass('water', 100);
const mg2 = mg1.takeDrink(20)

console.log(mg1, mg2)
console.log(mg1 === mg2)
console.log(mg1.amount == mg2.amount)


class ImmutableGlass {
    constructor(content, amount) {
        this.content = content;
        this.amount = amount;
    }
    takeDrink(value) {
        return new ImmutableGlass(this.content, Math.max(this.amount - value, 0))
    }
}

const ig1 = new ImmutableGlass('water', 100);
const ig2 = ig1.takeDrink(20)
console.log(ig1, ig2)
console.log(ig1 === ig2)
console.log(ig1.amount == ig2.amount)

partialAplication.js

// Partial Application

const fetch = require('node-fetch')
const getFromAPI = baseUrl => endpoint => cb => 
    fetch(`${baseUrl}${endpoint}`)
    .then(res=> res.json())
    .then(data=> cb(data))
    .catch(err=>{
        console.error(err.message);
    })
const getGithub = getFromAPI('https://api.github.com')

const getGithubUsers = getGithub('/users')
const getGithubRepos = getGithubUsers('/repositories')

getGithubUsers(data => {
    console.log(data.map(user => user.login))
})
getGithubUsers(data => {
    console.log(data.map(user => user.avatar_url))
})

pointfreeProgramming.js

const array = [1,2,3]
// array.map( x => x * 2) 
const double = x => x*2;
array.map(double)
// Legibility
// Reduce surface area 
// Unit test our named functions

pureFunction.js

// f(x) = x + 1
const f = x => x+1;

// EX 1 global state

const COST_OF_ITEM = 19
const cartTotal = quantity => COST_OF_ITEM * quantity;

console.log(cartTotal(2))
console.log(cartTotal(2))

// EX 2 same input different output
const generateID = () => Math.floor(Math.random() * 10000)

console.log(generateID())
console.log(generateID())
console.log(generateID())

const createUser = (name, age) => ({
    id: generateID(),
    name,
    age
})

console.log(createUser('hamza', 32))
console.log(createUser('hamza', 32))
console.log(createUser('hamza', 32))

// for fixing the different id generation

// EX 3 side effects#1
let id = 0
const createFoodItem = name => ({
    id: ++id,
    name
})
console.log(createFoodItem('CheeseBurger'))
console.log(createFoodItem('Fries'))
console.log(createFoodItem('Coke'))
console.log(createFoodItem(id))